1. Field of the Invention
This invention relates to apparatus relieving the pressure of arc gases that builds up in arc chutes of electric power switches during current interruption and to electric power switches incorporating such arc chutes.
2. Background Information
Electric power switches in which the contacts are exposed to air and that are designed to open circuits carrying appreciable current typically experience arcing as the contacts separate. These electric power switches, such as for instance, circuit breakers, commonly incorporate arc chutes to help extinguish the arc. Such arc chutes typically comprise a number of electrically conductive plates held in spaced relation around the separating contacts by an electrically insulative housing. The arc transfers to the arc plates where it is stretched and cooled until extinguished. A considerable volume of gas is generated by the arc. The pressure generated by this arc gas must be relieved to avoid catastrophic damage to the switch casing. However, this discharge of the arc gas must be controlled to avoid injury to persons nearby and to prevent phase to ground or phase to phase arcing in multiphase switches. Various arrangements for venting arc gases from electric power switches have been proposed. However, there is still room for improvement.
This invention is directed to an arc chute with a valve and to electric power switches incorporating such an arc chute. The arc chute comprises an arc chute chamber structure with a gas opening for releasing arc gases generated during contact separation. The valve comprises a flexible sheet member mounted at its two ends to the arc chamber structure to extend over and close the gas opening in the absence of arc gases. At least one of the two ends of flexible sheet member is free to slide along the arc chamber structure and bow the flexible sheet member between the two ends allowing arc gases to pass outward from the gas opening. The electric power switch incorporating this arc chute has a casing with a gas vent through which the arc gases released through the valve pass out of the casing.
More particularly, the invention is directed to an arc chute for an electric power switch that generates arc gases upon opening. The arc chute comprises an arc chamber structure having at least one gas opening for releasing arc gases and a valve. The valve comprises a flexible sheet member having two ends and side edges extending between the two ends, and mounting means mounting the flexible sheet member at the two ends to the arc chamber structure to extend over and close the at least one gas opening in the absence of arc gases. At least one of the two ends of the flexible sheet member is free to slide along the arc chamber structure and bow the flexible sheet member between the two ends allowing arc gases to pass from the gas opening out laterally between the side edges of the resilient member and the arc chamber structure. The mounting means can comprises a guide on the arc chamber structure slideably engaging the at least one end of the sheet member to allow it to slide along the arc chamber structure. The mounting means can further comprise at least one longitudinal slot through the one end of the flexible sheet member. In this case, the guide on the housing slideably engages the longitudinal slot to allow the one end of the flexible sheet member to slide. The mounting means can comprise a pair of laterally spaced longitudinal slots through the one end of flexible sheet member and a pair of guides on the arc chamber structure slideably engaging the pair of longitudinal slots. The second end of the flexible sheet member can be similarly mounted by the mounting means for sliding.